The Unit on Organelle Biology at CBMB studies the mechanisms underlying the spatial organization, distribution and dynamics of the membranes comprising the central vacuolar system (including ER, Golgi, lysosomes and endosomes). Because processes regulating membrane traffic and membrane-cytoskeletal interactions both play fundamental roles in establishing and maintaining the optimal organization and distribution of these membranes within cells, research in this unit bridges what historically has been two largely distinct lines of research- membrane trafficking and microtubules. Over the past year this unit has focused on the ER/Golgi membrane system of higher eukaryotes as a model for investigating the specific roles played by microtubules, microtubule motors and membrane traffic components in determining the distribution of organelles. Using a combination of biochemistry, microscopy and image analysis we have found that: 1) microtubules play an important role in directing membrane transport between the ER and Golgi complex; 2) the forward and reverse membrane transport pathways connecting the ER and Golgi complex play a role in determining Golgi localization and remodeling within cells due to constitutive cycling of Golgi resident components along these pathways; 3) the microtubule motor kinesin serves as the plus end-directed motor for Golgi-to-ER transport and cycles with membrane between the ER and Golgi complex; and 4) there are signal dependent mechanisms for regulating the extent of Golgi structure and function within primitive eukaryotes.